The present invention relates to a control device and method for an internal combustion engine equipped with a fuel injection system; and more particularly relates to a control device, incorporating a plurality of sensors and an electronic control computer which receives signals from said sensors and which controls said fuel injection system of said internal combustion engine, said control device accurately and appropriately controlling the amount of fuel supplied by said fuel injection system during various and diverse operational conditions of the internal combustion engine so as to provide good engine operational characteristics, and to a control method for said internal combustion engine equipped with a fuel injection system, said control method being practiced by said device.
Fuel injection is becoming a more and more popular method of fuel supply to gasoline internal combustion engines of automotive vehicles nowadays. This is because of the inherently greater accuracy of metering of liquid fuel by fuel injection techniques as opposed to the metering of liquid fuel available in a carburetor type fuel supply system. In many cases the advantages obtained by this greater accuracy of fuel metering provided by a fuel injection system outweigh the disadvantage of the increased cost thereof. For example, this better fuel metering enables engine designers to produce engines with higher compression ratio and more spark advance, which can lead to increased performance characteristics, such as increased power, increased torque, and better engine elasticity.
Because a fuel injection system can accurately determine the amount of fuel to be supplied to the airfuel mixture intake system of the vehicle in a wide variety of engine operational conditions, it is possible to operate the engine in a way which generates substantially lower levels of harmful exhaust emissions such as NOx, HC, and CO; and in fact it is possible to satisfy the legal requirements for cleanliness of vehicle exhaust, gases, which are becoming more and more severe nowadays, without providing any exhaust gas recirculation for the engine. This is very beneficial with regard to drivability of the engine, especially in idling operational condition. Further, because of the higher efficiency of fuel metering available, this allows leaner airfuel mixture operation of the engine with still acceptable drivability. With fuel injection provided to a vehicle type, more consistent exhaust emission results are available from vehicles coming off the assembly line at the factory, without complicated, troublesome, and expensive individual adjustments. Further, the warmup control of the vehicle is highly flexible, i.e. can be flexibly adjusted to a wide variety of engine warming up conditions, which contributes considerably to the achieved exhaust emission results.
Further, an internal combustion engine equipped with a fuel injection system can be operated in such a way as to be substantially more economical of gasoline than a carburetor type internal combustion engine. This is again because of the greater accuracy available for determination of the amount of fuel to be supplied to the intake system of the vehicle over a wide variety of engine operational conditions. Since it is possible to operate the engine at the stoichiometric air/fuel ratio, and to apply closed loop control to the fuel injection control system, it is possible to reduce the amount of spark retardation, and also the above mentioned dispensing with exhaust gas recirculation is possible, and both of these have significant beneficial effects with regard to fuel consumption. Further, with a fuel injection type fuelair mixture supply system, it is possible to cut off fuel supply entirely when the engine is operating in an overrun mode, which again results in a significantly reduced consumption of fuel. Nowadays, with the increased cost of fuel and the wider demand for fuel economical vehicles, and with legal requirements which are being introduced in some countries relating to fuel economy of automotive vehicles, these considerations are more and more becoming very important. In addition, by the introduction of a fuel injection type fuel-air mixture supply system, a engine of smaller piston displacement can replace an engine with larger piston displacement which is provided with a carburetor type fuel supply system, while providing the same output power, and again this reduces fuel consumption. By the introduction of a fuel injection type fuel-air mixture supply system, also, in many cases it is possible to switch an engine from premium grade type fuel operation to operation on lower grade or regular type fuel, while still providing the same output power, which is economical of the more expensive premium grade type fuels.
Some types of fuel injection system for internal combustion engines utilize mechanical control of the amount of injected fuel. An example of this mechanical fuel amount control type of fuel injection system is the so called K-jetronic type of fuel injection system. However, nowadays, with the rapid progress which is being attained in the field of electronic control systems, various arrangements have been proposed in which electronic control circuits make control decisions as to the amount of fuel that should be supplied to the internal combustion engine, in various engine operational conditions. Such electronic fuel injection systems are becoming much more popular, because of the more flexible way in which the fuel metering can be tailored to various different combinations of engine operational conditions. The most modern of these electronic fuel injection systems use a microcomputer such as an electronic digital computer to regulate the amount of fuel injected per one engine cycle, and it is already conventionally known to use the microcomputer also to regulate various other engine functions such as the provision of ignition sparks for the spark plugs.
In an electronic fuel injection system, the control system requires of course to know the moment by moment current values of certain operational parameters of the internal combustion engine, the amount of injected fuel being determined according to these values. The current values of these operational parameters are sensed by sensors which dispatch signals to the electronic control system via A/D converters and the like. In such an arrangement, electric signals are outputted by such an electronic control system to an electrically controlled fuel injection valve, so as to open it and close it at properly determined instants separated by proper time intervals; and this fuel injection valve is provided with a substantially constant supply of pressurized gasoline from a pressure pump. This pressurized gasoline, when the fuel injection valve is opened, and during the time of such opening, is squirted through said fuel injection valve into the intake manifold of the internal combustion engine upstream of the intake valves thereof. Thus, the amount of injected gasoline is substantially proportional to the time of opening of the fuel injection valve, less, in fact, an inoperative time required for the valve to open. Sometimes only one fuel injection valve is provided for all the cylinders of the internal combustion engine, or alternatively several fuel injection valves may be provided, up to one for each cylinder of the engine, according to design requirements.
The first generation fuel injection systems were of the so called D-jetronic type, in which the main variables monitored by the electronic fuel injection control system are the revolution speed of the internal combustion engine and the vacuum, or depression, present in the intake manifold of the internal combustion engine downstream of the throttle valve mounted at an intermediate position therein due to the suction in said intake manifold produced by the air flow passing through the intake manifold of the internal combustion engine to enter the combustion chambers thereof after being mixed with liquid fuel squirted in through the fuel injection valve or valves. From these two basic measured internal combustion engine operational parameters, a basic amount of gasoline to be injected into the intake system of the internal combustion engine is determined by the control system, and then the control system controls the fuel injection valve so as to inject this amount of gasoline into the engine intake system. Other variables, such as intake air temperature, engine temperature, and others, are further measured in various implementations of the D-jetronic system and are used for performing corrections to the basic fuel injection amount.
Following this, a second generation of fuel injection systems has been developed, which is of the so called L-jetronic type, in which the main variables monitored by the electronic fuel injection control system are the revolution speed of the internal combustion engine and the amount of air flow passing through the intake manifold of the internal combustion engine to enter the combustion chambers thereof after being mixed with liquid fuel squirted in through the fuel injection valve or valves. This air flow amount is measured by an air flow meter of a design which has become developed, located at an intermediate point in the intake manifold. From these two basic measured internal combustion engine operational parameters, again a basic amount of gasoline to be injected into the intake system of the internal combustion engine is determined by the control system, and then the control system controls the fuel injection valve so as to inject this amount of gasoline into the engine intake system. Other variables, such as intake air temperature, engine temperature, and others, are again further measured in various implementations of the L-jetronic system, and are used for performing corrections to the basic fuel injection amount. This L-jetronic fuel injection control system is currently well known and is nowadays fitted to a large number and variety of vehicles.
One refinement that has been made to the L-jetronic fuel injection system has been to perform a control of the fuel injection amount based upon feedback from an air/fuel ratio sensor or O2 sensor, which is fitted to the exhaust manifold of the internal combustion engine and which detects the concentration of oxygen in these exhaust gases, again in a per se well known way. This feedback control homes in on a proper amount of fuel injection, so as to provide a stoichiometric air/fuel ratio for the intake gases sucked into the cylinders of the engine, and for the exhaust gases of the engine, but the starting point region over which the homing in action of such a feedback control system is effective is limited, and therefore the determination of the approxmately correct amount of fuel to be injected by the fuel injection valve is still very important, especially in the case of transient operational conditions of the engine.
A typical kind of air flow meter that is used in the L-jetronic system of fuel injection engine control system is illustrated in sectional view in FIG. 3 of the appended drawings. Such an air flow meter has a flapper element, biased in the rotational direction to obstruct the air intake passage, which is thus displaced in the opposite rotational direction according to the air flow amount that is being aspired into the internal combustion engine. The movement of this flapper element is sensed by some sensing system such as a potentiometer, and is damped by some damping system such as for example the one shown in the figure, which is a pneumatic type damping system.
A difficulty that has occurred with such a type of air flow meter is that such a flapper element tends to overshoot its proper position during the initial phase of sharp acceleration of the internal combustion engine, so that at this time the above mentioned air intake flow amount sensing system such as a potentiometer indicates, for a short transient time immediately after start of acceleration, a substantially greater value for intake air amount than the correct amount. It will of course be appreciated by those skilled in the art that, if the amount of fuel injected through the fuel injection valve into the intake manifold is based directly upon this erroneous signal provided by the overshooting flapper element which actuates the above mentioned air intake flow amount sensing system such as a potentiometer, then during this overshooting time, just after the start of engine acceleration, too much fuel will be supplied to the internal combustion engine, and a rich spike will be caused in the air-fuel mixture supplied to said engine. This will cause considerable variation of the acceleration being provided by the internal combustion engine, i.e. will cause jerk or torque shock during the initial phase of acceleration. Further, it has been found that merely increasing the amount of damping of the movement of the flapper element provided by said damping means such as a pneumatic damping system is not adequate to solve this problem, since over damping of the movement of said flapper element is unduly restrictive of its movement. This rich spike in the the air-fuel mixture supplied to said engine dies away quickly with time, after the initial start of acceleration.
Another difficulty that has occurred with such normal spark ignition engines which are equipped with the L-jetronic form of electronic fuel injection system is that, if the fuel injection system calculates the amount of fuel which it is desired to inject into the combustion chambers of the engine in the next pulse of fuel injection, and then simply controls the fuel injection valve or valves in the engine air intake system so as to inject this amount of fuel into the air intake system on this next fuel injection pulse, the engine will be substantially properly operated during steady operational conditions, but during the initial phase of acceleration the engine will not receive the proper amount of fuel, because of the effect of fuel adhering to the wall surfaces of the air intake passage and of the intake ports of the engine.
Considering this phenomenon in more detail, since in such a L-jetronic fuel injection system the supply of liquid fuel is not vaporized or finely atomized as in a carburetor type fuel supply system, but is squirted directly into the air intake passage of the engine through the fuel injection valve which cannot atomize the fuel very well, therefore quite a large quantity of liquid fuel tends to accumulate in liquid form on the wall surfaces of the air intake passage and of the intake ports. Of course, also some of this liquid fuel tends to get swept off or sucked off these wall surfaces into the combustion chambers of the engine. In completely steady state operation of the engine, these two effects, i.e. the fuel accumulation or adhering effect and the fuel sucking off effect, tend to cancel one another out. However, during rapidly changing operational conditions of the engine, such as sharp acceleration of the engine, these two effects by no means cancel one another out, and prior art types of fuel injection systems in which no consideration was given to the effect of adhesion of fuel on the wall surfaces of the air intake passage and of the intake ports, and the effect of sucking off of said fuel, are not able to provide proper operation of the internal combustion engine, during such sharp acceleration conditions.
In detail, in the prior art type of fuel injection system in which no consideration is given to the effect of adhesion of fuel on the wall surfaces of the air intake passage and of the intake ports, and to the effect of sucking off of said fuel, when the engine is accelerated of course the throttle valve in the air intake system is opened, and together with this the amount of fuel being injected through the fuel injection valve is simultaneously increased; but, because a substantial proportion of this extra injected fuel is adhered or accumulated in the liquid layer or film on the wall surfaces of the air intake passage and of the intake port, thus increasing the total volume of fuel in this liquid layer or film, thereby the air-fuel mixture actually being supplied into the combustion chambers of the internal combustion engine becomes over lean; in other words, a lean spike of air-fuel mixture occurs during engine acceleration, in fact somewhat after the start of such acceleration.
An aggravating factor with regard to these two problems during engine acceleration, i.e. the problem of the occurrence of an initial rich spike of air/fuel ratio caused by overshooting of the air flow meter, and the problem of the occurrence of a somewhat delayed lean spike of air/fuel ratio caused by accumulation of fuel in the liquid layer or film on the wall surfaces of the air intake passage and of the intake port, is due to the timing of these spikes. In fact, the first rich spike due to overshooting of the air flow meter tends to occur just before the second lean spike due to adherence of fuel to said wall surfaces, and the combined or synergistic effect of these two contrary spikes tends to produce a much worse jerking performance of the internal combustion engine during acceleration, than would occur because of either the rich spike or the lean spike, on its own.
This effect is illustrated in FIGS. 8 and 9 of the appended drawings. FIG. 8 is a time chart, in which air/fuel ratio of air-fuel mixture actually delivered to the combustion chambers of the internal combustion engine is shown on the ordinate and time is shown on the abscissa, showing by the single dotted line the behavior of variation of air/fuel ratio of the air-fuel mixture of an engine with a fuel injection system controlled according to a prior art method of engine control, during an engine operational episode involving sharp acceleration. This figure illustrates that during steady operation of the internal combustion engine the air/fuel ratio of the air-fuel mixture in this engine controlled in a prior art fashion is substantially stoichiometric, but that during sharp acceleration of the engine the air/fuel ratio of the air-fuel mixture in this engine controlled in such a prior art fashion deviates substantially from stoichiometric first towards the rich side and then immediately subsequently towards the lean side, i.e. undergoes in rapid succession first a rich spike and then a lean spike. Further, FIG. 9 is a time chart, in which vehicle acceleration is shown on the ordinate and time is shown on the abscissa, said abscissa corresponding to and indicating the same time as the abscissa of FIG. 8, showing by the dashed line the behavior of variation of vehicle acceleration of said vehicle incorporating said internal combustion engine with a fuel injection system controlled according to said prior art method of engine control, during the same sharp acceleration engine operational episode as the engine operational episode illustrated in FIG. 8. This figure shows that when this vehicle incorporating this internal combustion engine with a fuel injection system controlled according to said prior art method is sharply accelerated, it undergoes very sharp variation of acceleration, i.e. jerk or lurching, which is very uncomfortable for riders in the vehicle, and reduces vehicle drivability, as well as impairing durability of the engine and of the transmission of the vehicle, which transmits the power of said engine to the road surface. Further, the presence of the above described rich spike and of the above described lean spike of air/fuel ratio of the air-fuel mixture supplied to the combustion chambers of the internal combustion engine are liable to cause problems with regard to meeting the ever more strict standards with regard to purification of the exhaust gases of the internal combustion engine.
In order to investigate the problems with regard to the amount of fuel adhering to the wall surfaces of the intake manifold and the intake ports, one of the present inventors, together with another, has carried out various experimental researches relative to the behavior of fuel, both in its adhering to said wall surfaces of the air intake passage and of the intake ports, and in its being sucked off from said wall surfaces by the air flowing therepast, so as to enter into the combustion chambers of the engine. Some of the results of these experimental researches may be summarized as follows. The amount of fuel out of one pulse of fuel injection provided through the fuel injection valve which adheres to the wall surfaces of the air intake passage and of the intake ports, so as to be added to the cumulative amount of fuel already there, is, other things being equal, roughly proportional to the total amount of fuel in said fuel injection pulse; in other words, substantially the same proportion of the injected fuel tends to adhere to said wall surfaces, irrespective of the actual amount of injected fuel. The proportionality constant relative to this adhesion, however, tends to vary with variation of, in particular, the following quantities: air intake manifold pressure or depression, engine cooling water temperature, engine revolution speed, and air flow speed in the air intake manifold. As a matter of fact, said proportionality constant varies, to a lesser extent, with intake passage wall temperature and intake air temperature and atmospheric pressure. Further, the absolute amount of fuel out of the total or cumulative amount of fuel which is adhering to the wall surfaces of the air intake passage and of the intake ports which is sucked off into the combustion chambers of the internal combustion engine is, other things being equal, roughly proportional to said total or cumulative amount of fuel adhering to the wall surfaces of the air intake passage and of the intake ports; in other words, substantially the same proportion of the fuel adhering to the wall surfaces tends to be sucked off, irrespective of the actual amount of adhering fuel. The proportionality constant relative to this sucking off, however, again tends to vary with variation of the following quantities: air intake manifold pressure or depression, engine cooling water temperature, engine revolution speed, and air flow speed in the air intake manifold. Again, as a matter of fact, said proportionality constant varies, to a lesser extent, with intake passage wall temperature and intake air temperature and atmospheric pressure. Further details of these experimental researches performed by the present inventor, and another, with respect to these proportionality constants will be found later in the section of this specification entitled "DESCRIPTION OF THE PREFERRED EMBODIMENT".